<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        
    </style>
</head>
<body>
    
</body>
<script>
    // 89小时，转成n天零n小时

    var hours = 89;

    // var d = parseInt(hours / 24);
    // var h = hours%24;

    var h = hours % 24;
    var d = (hours - h)/24;

    console.log(d + "天" + h + "小时");


    // ================

    var h = 80;
    var s = 5 / 9.0 * (h - 32);
    console.log(s.toFixed(3))


    // ================

    var c = 5;
    var sum = c++ + ++c + c-- + c++ + --c + c-- + ++c + c++;
    console.log(c);     // 7
    console.log(sum);   // 49

    // ================

    // 圆的面积：pai * r * r
    var r = 80;
    var pai = 3.1415;
    var s = pai * r * r;
    document.write("半径为80的圆的面积为：" + s);

    document.write("<hr>")

    // 圆的周长：2 * pai * r
    var c = 2 * pai * r;
    document.write("半径为80的圆的周长为：" + c);

    // ================
    // 角度转弧度，公式：
    // jiao = 180 / pai * hu
    // hu = jiao / (180 / pai)

    // 15 = 9 / 3 * ?
    // ? = 15 / (9 / 3)

    var deg = 90;
    var hu = deg / (180/pai);
    console.log("角度90转成弧度之后为：" + hu);





</script>
</html>